Theanine is well acknowledged as a main component of green tea flavor substance, and therefore, is an important component of food essence. In addition, γ-glutamyl derivatives including theanine were reported to suppress convulsion induced by caffeine intake (Chem. Parm. Bull., 19(7), 1301-1307 (1971). ibid.19(6), 1257-1261 (1971). ibid.34(7), 3053-3057 (1986). YAKUGAKUZASSHI 95(7), 892-895 (1975) ).
These results suggest that the compounds act on central nervous system, and therefore, these compounds are hoped for useful bioactive substances.
It is a common practice to produce theanine by extracting the substance from dry tea (Gyokuro) leaves. However, theanine is stored in the leaves but only up to 1.5% of the dry weight. In addition, theanine is rapidly degraded in the commercial tea trees by the active photosynthesis, and therefore theanine can hardly be obtained in commercial tea fields. Thus, extraction of theanine from dry tea leaves is recognized an impractical method industrially.
The difficulty in obtaining theanine at the industrial scale lead to development of new production methods such as to synthesize theanine chemically (Chem. Par. Bull., 19(7), 1301-1308 (1971). The chemical synthesis methods, however, include complicated purification steps and do not produce high yield of theanine. An enzymatic method was also reported (JP,H07-55154,B), wherein theanine is synthesized enzymatically from glutamine and ethylamine by exploiting γ-glutamyl group transfer activity of glutaminase However, glutamic acid produced by glutaminase in parallel with theanine makes purification of theanine complicated.